The Performance Assessment and Remedial Measures of Bridge Structure

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Addis Ababa University


The bridge is an infrastructure which built across the river also used to pass safely from one side of the road to another to cross the river; on the road shall be kept strong to serve intended purposes. The bridge structure requires detail, assessment before and after construction both due to possible failures. Many countries have come upon different mitigation measure to overcome failure by providing bridge assessment. Ethiopian Road Authority follows up bridge structure failure by recording all necessary data about bridge and Road situation. The Bilate River Bridge is the one among those encountered local abutment failure. The abutment failure of the bridge was seen at different times, which is observed in the field assessment. The analysis was conducted on the abutment scour failure for a different return period of time. The existing bridge opening size was the 26m length, 5m wide. Both sides of riverbank material were taken and analysis is done in a laboratory result express that particle diameter of 1.5mm and 34.5mm for D50 and D95 respectively. The maximum design flood estimation resulted in 284.2m 3 /s, and 327.3 m 3 / at the Bilate River for 50-year and 100-year return period respectively. In the design flood estimation rainfallrunoff model analyzed by Initial and constant loss method and direct runoff by the SCS unit hydrograph method also base flow by recession method. The Bridge instability evaluated by HEC RAS 5.0.1; has been prepared by taking inputs like; river cross section, design flood, and riverbank materials. The local abutment scouring observed in the vicinity of the structure of the bridge incorporate with overtopping which endures Bridge to fail. The model results show that dominate cause of abutment scours of the bridge was an inadequate opening size to pass design flood at the bridge; because of constriction at the bridge within the river has resulted in an increase the flow velocity so that, the abutment has been scoured. Countermeasures were reviewed based on the hydraulic analysis result calculated. Based on hydraulic analysis results; the recommended river training work and increase the opening size of a bridge across the river.



Design Discharge, HEC-HMS, Hydraulic analysis, HEC-RAS, scour, Bilate, Bridge